Filter assembly



y 1954 H. F. GERWIG EFAL FILTER ASSEMBLY Filed Sept. 27, 1952 Patented July 27, 1954 Harvey F. Gerwig, Glendale,

Burbank, Cyril W. Fr

Frederick '0.

Percy A. Jameson,

anklin, Glendale, and Hostel-man, Burbank, Califi, as-

signors to Weston Hydraulics, Limited, North Hollywood, Calif., a corporation of California Application September 27, 1952, Serial No. 311,868

3 Claims. 1

This invention relates generally to filters, and more particularly to a filter assembly for installa== tion directly within a hydraulic control valve or the like.

Complex hydraulic systems such as are found in modern aircraft for operating control surfaces are conventionally equipped with system filters to remove dirt, sediment and'other foreign matter from the hydraulic fluid. These system filters are often a considerable distance from actuating con= trol valves or similar elements, and the interposition of joints, couplings, and other component elements of the system makes possible the entrance of foreign matter ahead of the system filter.

To avoid high pressure leaks, the operating members within a control or power valve are often lap fitted to extremely fine tolerances on the order of several millionths of an inch. If any small particles of foreign matter are carried by the hydraulic fluid and these flow into the immediate area of the closely fitted par-ts, frictional binding may occur and the valve will .jam or stick. To overcome this difiiculty it is desir able to locate a filter assembly directly within the control unit in a position to protect the closely fitted parts. Such an assembly must be of compact design adapted to be conveniently installed and removed, and operable without causing an excessive pressure drop.

The filter assembly herein disclosed is designed for installation on a form of hydraulic operating member which is a common element of many dil ferent hydraulic units. Typically, the operating member takes the vform of a generally tubular control casing, or sleeve having radial ports com municating with a central longitudinal bore. Within said bore is a relatively movable element, as for example a slidable control shuttle which is lap fitted to an extremely close tolerance with the Wall of the bore. The filter assembly is re movably fitted into an annular groove surrounding the radial ports and prevents the passage of any fine particles interiorly so as to protect the movable element. It is to be understood, or course, that the filter assembly can be used in many different hydraulic units and is not limited to any particular installation.

With the foregoing in mind, it is a major object of the invention to provide a compact filter assembly which may be installed directly within conventional hydraulic units without modification thereof.

Another object of the invention is to provide a filter assembly which is adapted to be fitted 2 into a continuous annular groove and to be held securely therein.

It is also an object of the invention to provide a filter assembly utilizing the maximum available filtration surface, and which is operable without causing a large pressure drop.

A further object of the invention is to provide a filter assembly having a filter element which traps foreign matter therein upon inward flow and is adapted to be flushed clean upon back or reverse flow.

It is a still further object of the invention to provide a filter assembly including an inner expander ring and an outer clamping band to securely position an intermediate filter element of split or two-part construction.

Still another object of the invention is to provide a filter assembly which may be economically constructed and easily modified for different installations.

These and other objects and advantages of the invention will become apparent from the following detailed description of a preferred form thereof, and from an inspection of the accompanying drawings, in which:

Fig. 1 is a perspective view of a typical hydraulie operating member showing the filter assembly installed thereon;

Fig. 2 is a cross-section taken in the direction of the arrows 2'-2 of Fig. 1;

Fig. 3 is an enlarged radial section through the filter assembly taken along the line 3--3 of Fig. 2;

Fig. 4 is an enlarged cross-sectional detail showing the clamping ring in a partially applied position;

Fig. 5 is an exploded view showing the elements of the filter assembly; and

Fig. 6 is an enlarged partial elevation of the filter element.

Referring now to the drawings. and particu larly to Fig. .1 thereof, the numeral 10 designates a typical operating member of a hydraulic unit on which the filter assembly may be installed. The member to is formed as a generally tubular sleeve having an interior axially extending bore 1 l. on the exterior surface of the member in are spaced-annular grooves I? which are separated by lands 13 that form the side walls of the grooves. Within each groove 12 is a set of radially directed ports I4 that open inwardly through the Wall of member In and communicate with bore H.

The member it thus shown is by way of'illustration, and is representative of a type of operatingapart well known to those skilled in the hydraulic art. In a conventional unit, member l0 is fitted within the valve chamber of a valve housing and grooves |2 are opened to various external ports. Bore H is adapted to receive a control shuttle or like element (not shown) which is slidably mounted therein and is relatively movable for effecting different port interconnection. At one position of the shuttel, a particular annular groove 12 may direct fluid inwardly from an external pressure source through ports l i into bore ll. At another shuttle position, the flow of fluid may be reversed so that fluid passes outwardly through ports M into grooves l2. In a high pressure unit where fine control is to be achieved, such a sliding element would be closely fitted within the wall of bore l| so that the smallest particle of foreign matter could cause binding friction. In order to prevent such friction and insure proper functioning of the device, a preferred embodiment of the filter assembly 28 is mounted within each of the annular grooves |2 to block the passage of any particles into ports I4. As shown in Fig. l, the filter assembly 28 lies entirely within groove l2 and does not in any way interfere with the normal operation of the unit.

Filter assembly 20 comprises a filter element 2| which is supported between an inner perforate expander 22 and an outer clamping band 23 as is seen in Fig. 2. The filter element 2| is designed to accomplish the filtration of hydraulic fluid entering into ports l t by trapping and holding any foreign porticles which may be suspended Within the fluid. Because the filter element must be fitted within the continuous annular groove l2, and in order to prevent a large pressure drop across the assembly, the filter element is specifically designed to have a cooperative relationship with the inner expander 22 and clamping band 23, as will hereinafter be described.

Filter element 2| is formed as an annular ring having a plurality of small edge openings which pass through the filter generally perpendicular to the axis thereof. As can be understood, if element 2| is to operate without causing undue restriction upon the fluid flow, the surface area of the filtration openings must be a large part of the total exterior surface. At the same time, the size of each individual opening must be small enough so that particles of foreign matter cannot pass therethrough. To provide a ring having such characteristics; element 2| is formed of a strip of relatively stiff metal wound into a helical coil having the turns thereof spaced slightly apart. As is best seen in Fig. 3,'the strip from which element 2| is wound is of generally rectangular cross-section having a thin outer edge 24 lying parallel to the axis of the coil, and elongated sides 25 extending generally perpendicular thereto. An inner edge surface 26 is slightly wider than outer edge 24 so that sides 25 have a small angle of convergence in the outward direction.

In order to space the adjacent coil turns apart, side bosses 21 are spaced circumferentially along one of the sides 25, as is-best seen in Figs. and 6. Bosse 21 are adapted to lie against the adjacent side 25 of the next turn of the coil to define openings 28 which extend edgewise through the element. To prevent separation of the turns, bosses 21 may be brazed or otherwise secured along the sides 25 of the adjacent turn to form a rigid unitary structure. As will be noted, the circumferential length of bosse 21 is relatively small as compared to the length of the opening 28, and the edge thickness 24 of the strip is as thin as possible. In this way, the total area of the filtra tion openings becomes a relatively large part of the outer surface area of the element and the fluid flow is not unduly restricted.

Because of the forwardly convergent shape of sides 25, the width ofopenings 28 decreases rearwardly in section as is seen in Fig. 3. Foreign particles of a very small size are therefore caught and wedged between sides 25 so as to be held from passing inwardly into ports M. The minimum width of openings 28 is so small that particles which may pass therethrough are of no practical danger. As was previously mentioned, while the normal direction of flow is inwardly, it is a common feature of hydraulic units to provide for reverse or back flow so that the fluid passes outwardly through ports l4. When thi occurs, the particles trapped within element 2| are flushed clear so that the surface of the element does not become clogged or permanently blocked.

While the maximum number of openings 28 are provided, their collective area is necessarily somewhat smaller than the total surface area of the element 2|. However, by the use of perforate expander 22 in combination with element 2|, it is possible to prevent any excessive pressure drop due to the reduced opening area. As can be appreciated, the maximum fluid flow into bore II is determined by the pressure of the fluid and the collective cross-sectional area of ports M. Fromv the nature of the structure it is also apparent that this area is again considerably less than the total surface of element 2|. Therefore, if all of the openings 28 through element 2| are effective to permit fluid flow, the useful opening area may be substantially equal to the collective area of ports l4. Under this condition, little or no pressure drop will be caused by the use of the filter assembly.

Expander 22 is formed from a corrugated strip of deformable metal having an undulating or sinusoidal edge profile bent into an annular closed ring which seats within the bottom of groove l2. Enlarged openings or perforations 30 are spaced about the circumference of expander 22 to provide for free fluid flow therethrough. Preferably, perforations 30 are so spaced with relation to the corrugations of expander 22 that the center line of each perforation extends through the bottom portion or trough of the corrugations adjacent the bottom wall of groove l2. In this way the interconnecting webs of material between the perforations 3G lie on the ridges along the outer surface of expander 22 and are positioned to rigidly support element 2 L It should also be noted that because of the raised position of the interconnecting webs, fluid may flow between perforations so along a circumferential path.

Since the formed filter element 2| as thus far described is a rigid closed ring, it is necessary that provision be made for fitting this element into the continuous annular groove l2. To this end, element 2| is split into semi-circular upper and lower halves 2 la and 2 lb, respectively, which can be conveniently seated upon the outer surface of expander 22. Preferably, expander 22 is made slightly oversize so that the abutting ends of element halves 2 la and 2 lb are initially spaced slightly apart. Then, as clamp 23 is subsequently positioned around element 2|, the ends of the element halves are brought together by spring deformation of expander 22. This tightly secures the assembly together to prevent any play therein and also binds the assembly non-rotatably within groove l2.

ass-4m element 2| seated upon the expander 2, flowing through any of the element openings 28 passes through enlarged perforations 30 in generally radial direction. Because of the corrugated nature of expander 22, the fluid may then travel ,annularly along the surface of groove l2 until it reaches one of the ports I4. Thus, in raising element '21 from the surface of groove l2, expander 22 makes effective substantially the total area of all of the openings 28. Since this area may compare favorably with the effective area of ports l4, little or no pressure drop is occasioned by the use of the filter assembly, and the hydraulic operating pressures are not changed.

Clamp 23 is formed of a deformable band or strap having spaced apertures 32 therein, as is best seen in Fig. 5. The total area of apertures 32 is sufficiently large to permit a substantially free flow of fluid into element 2|. As was previously mentioned, clamp 23 is designed to bear tightly inwardly against element 2| and clamp the same tightly against expander 22. For the purpose of interlocking the ends of clamp 23 and at the same time drawing the clamp up tightly against element 2|, an overlapping seam or connection is formed in the ends of the clamp, as may best be seen with reference to Fig. 4.

One end of clamp 23 is brought around the filter element and then turned outwardly to provide an outstanding lip portion 33. The other end of clamp 23 is brought around the filter element and turned outwardly to form an elongated terminal portion which is then bent :back upon itself around the end of lip 33 to form a U-shaped flange 34 which brackets lip 33. The three layers of clamp material thus held together are then pressed downwardly to lie fiat against the surface of clamp 23 in the position shown in phantom outline. This causes flange 34 to be drawn upwardly so that clamp 23 is bound tightly about the filter element and placed under considerable tension. The completed seam, as shown in Fig. 2, is quite compact and lies well within groove |2 so as not to interfere with the operation of member Ill. It can also be appreciated that clamp 23 is thus secured without the use of special tools, to facilitate the replacement of element 2| should this become necessary.

While the preferred embodiment of the invention we have shown and described is particularly designed to carry out the aforementioned objects and advantages, it is to be understood that changes in design and construction may be made without departing from the scope of the invention. Therefore, we do not wish to be limited to the foregoing details of description, except as defined in the appended claims.

We claim:

1. In combination with a hydraulic operating member having an external annular groove and an internal port opening with said groove, a filter assembly which comprises: a rigid annular filter element formed in separable segments for installation within said groove, said element being built up of a strip of material of generally rectangular cross-section elongated in a direction perpendicular to the axis of said element and bent into turns spaced apart laterally to define a plurality of filtration openings throughout the surface thereof; an expander ring seated within the bottom of said groove and supporting said element thereon, said expander being corrugated and provided with perforations centered within the trough of the corrugations to allow both radial and circumferential flow, whereby fluid passing through any of said filtration openings may reach said port; anda clamp securedaround said filter element and having a plurality :of enlarged apertures therein allowing substantially free flow of fluid through said filter element, the ends of said clamp being brought together and bent into an overlapping seam pressed downwardly against said clamp to tension said element securely against said expander. I 2. In combination with a cylindrical member formed with an external annular groove having imperforate side walls and a port opening into the bottom of said groove, a filter assembly which comprises: a rigid annular filter element formed in separable segments for installation within said groove, said element being built up of a strip of material of generally rectangular cross-section elongated in a direction perpendicular to the axis of said element and having outwardly convergent sides with one of said sides carrying spaced bosses projecting laterally therefrom, and said strip being wound into helical turns spaced apart laterally by said bosses to define a plurality of inwardly convergent filtration openings throughout the surface thereof; an expander ring seated within the bottom of said groove and supporting said element thereon, said expander being corrugated and provided with perforations to allow both radial and circumferential flow, whereby fluid passing through any of said filtration openings may reach said port; and a clamp secured around said filter element and having a plurality of enlarged apertures therein allowing substantially free flow of fluid through said filter element, said clamp being formed as a deformable strap having the ends brought together and bent outwardly with one of said ends being bent around the other of said ends in a U-shaped flange, and said flange being pressed fiat against said clamp to draw said clamp inwardly and tension said element tightly against said expander.

3. In combination with a cylindrical member formed with an external annular groove having imperforate side walls and a port opening into the bottom of said groove, a filter assembly which comprises: an annular filter element formed in rigid separable segments for installation within said groove, said element being built up of a strip of material of generally rectangular crosssection elongated in a direction perpendicular to the axis of said element and having outwardly convergent sides with one of said sides carrying spaced bosses projecting laterally therefrom, and said strip being wound into helical turns held in spaced rigid alignment by securing said bosses to the side of an adjacent turn to define a plurality of inwardly convergent filtration openings throughout the surface thereof; an expander seated within the bottom of said groove and formed of a corrugated deformable ring having perforations therein centered Within the troughs of the corrugations to provide spaced interconnecting webs which extend across the ridges of the corrugations along the outer surface of the expander to support said element thereon, said perforations allowing both radial and circumferential flow, whereby fluid passing through any of said filtration openings may reach said port; and a clamp secured around said filter element and having a plurality of enlarged apertures therein allowing substantially free flow of fluid through said filter element, said clamp being formed as a deformable strap having the ends brought together and bent outwardly with one References Cited in the file of this patent UNITED STATES PATENTS Name Date Kneuper Sept. 14, 1909 Number Number Number Name Date James Apr. 27, 1915 Liddell June 2, 1936 FOREIGN PATENTS Country Date Great Britain of 1906 Great Britain Oct. 5, 1931 Great Britain Oct. 30, 1933 

